Method of and apparatus for amplifying electrical currents



June 5, 1928.

J. E. PARKER METHOD OF AND APPARATUS FOR AMPLIFYING ELECTRICAL CURRENTS Filed March 12, 1924 HHHO NO F the tuning of the resonant circuit.

Patented June 5, 1928.

RElSSU'ED 1,672,037 PATENT OFFICE.

JAMES E. PARKER, OF WASHINGTON, DISTRICT OF COLUMBIA.

METHOD OF AND APPARATUS FOR AMPLIFYING ELECTRICAL CURRENTS.

Application'filed March 12, 1924. Serial No. 698,680.

While my invention relates generally to the amplification of electrical currentsit has for a particular object the amplification of high frequency electrical currents modulated at low or audible frequency.

A particular object of the invention is the" eflicient amplification of the currents at high frequency and having so amplified the currents to reduce them to low frequencies and further amplifying the low frequency currents in the presence of the high frequency currents, using the same amplifying devices for the dual function.

My invention will be best understood by reference to the accompanying drawing in which it is illustrated in the figure employed as an amplifier in a receiving system for radio.

L represents a coil or loop receiver having a capacity tuning arrangement. illus-v trated by 0,. As the capacity G I preferably employ an air condenser having two sets of fixed plates and one set of movable plates. The movable plates .are controlled -by one shaft and since these plates are of a low potential at all times, I have grounded.

them as shown in order to eliminate any stray capacity effects in the manipulatiop of wo three-electrode vacuum tubes VT and VT, have their grids g and 9, connected to opposite sides of the capacity C The grounded filamentlead to these tubes is connected to approximately the mid point of the coil L through the secondary S of "audio frequency transformer AT This lead also includes a biasing battery 13,, to apply a negative potential to the leads of the vacuum tubes of a chosen value to obtain eflicient amplification. The plate circuits of tubes VT and VT are supplied with a source of energy B which causes currents "to fiow through choke coil I, and telephone receiver 1,, resistances R and R2, tuned circuit consisting of inductances L, and L,

with condensers C and C and through plates P and P back to filaments F and F 2 to battery B Inductively coupled to tuned circuit L L G, and C is another tuned circuit containing inductances L and con denser C One side of this tuned circuit is connected to filament F of a vacuum tube VT and the other side to the grid 9 The vacuum tube VT is connected for rectification, having stopping condenser SC and grid leak gL, and not including a biasing potential on the grid. The plate P, ofthis tube is connected to the source of energy B through the primary 2 of audio frequency transformer AT and the circuit is completed through the filament E The plate circuit connection to the battery B is shown as variable as the detector or rectifying tube does not require as much plate potential as do the amplifying tubes VT and V'l The filaments of the tubes are supplied with heating current from the battery A in the "usual manner. The condensers C and C are preferablyarranged as described in connection with capacity 0 The choke coil '1 is not essential but I find it preferable to permit a largercurrent flow in the plate circuit of the vacuum tubes VT and VT than pedance of telephones or loud speaking devices'I,. It is not essential to employ a tuned coupling between-the plate circuitsof vacuum VT and VT and the grid circuit of the vacuum tube VT the tuned coupling I have shown being replaceable by an ordinary radio frequency transformer or other is ordinarily obtainable through the imsuitable transfer device, but such devices are not as selective as the tuned coupling I have shown. The resistances R and R are for the purpose of restricting the tendency of the vacuum tubes to create oscillations in tuned circuits, and these resistances should be chosen of such value to just overcome this tendency so as not to destroy the amplitude of the amplified currents.

The operation of the system is as follows:

Signals are received on tune circuits L G acting as acollector. The signal currents being of an oscillatory nature charge grids g and 9 of the amplifier tubes VT and VT alternately with. equal and opposite potentials. By means of the biasing battery B the grids are worked at' a most efficient potential for amplification. The highly amplified currents are joined in the common plate circuit through the'connection between the inductances L and L This amplified current is in its high frequency form and is transferred to the detector tube VT by inductive coupling between coils L and L and resonant circuits L G In thevacuum tube VT the amplified currents are converted intolow frequency currents through the rectifying action of the tube and its connections, these low frequency currents being characteristic of the modulations in the high frequency currents. The low frequency ourlOO rents flowing through the plate circuit of the detector tube VT also flow through the primary or low 'frequency transformer AT and induce current in the secondary S of this transformer. This induced current then acts upon the grids g and g, of the amplifier tubes VT and VT causing these tubes to act as audio frequency amplifiers to actuate the telephones I with, amplified low frequency currents.

Having described my invention I claim:

1. The method of amplifyinghigh frequency electrical currents modulated at audible frequencies which consists of conelectrical currents modulated at low fre-- quencies to amplified low. frequency currents characteristic of said modulations which consists'of converting the said high frequency currents into opposite currents differing 180 degrees in phase with each other, employing the alternating high frequency potentials of said converted currents to produce amplified high frequency currents, combining the amplified currents, reducing the resultant amplified currents to low frequency currents corresponding to the modulations thereof, and amplifying said low frequency currents simultaneously with the amplication of subsequent h1gh frequency currents.

3. In a system for receiving and amplify ing electrical currents a pair of three electrode vacuum tubes, means for receiving high frequency -electrical 'currents, means for converting the said high frequency currents into opposite currents differing in phase with each other, means for applying the varying potentials of said opposite currents to the grids of said tubes, means for combining the resultant plate currents of said tubes, means for rectifying aid combined currentsto produce low frequency currents, and means for returning said low frequency currents to said vacuum tubes for further amplifi -ation in low frequency form.

4. In a system for receiving and amplifying electrical currents a pair of three electrode vacuum tubes, means for receiving high frequency electrical currents, means for converting the said high frequency currents into opposite currents differing 180 degrees in phase with each other, means for applying, the varying potentials of said opposite currents to the grids of said tubes, means for combining the resultant plate currents of said tubes, means forrectifying said com-' bined currents to produce low frequency currents and means for returning said low frequency currents to said vacuum tubes for further amplification in low frequency form.

5. In a receiving and amplifying system including a plurality of vacuum tubes having filaments, grids and plates and sources of power therefor, the combination of an input coil having a central tap, one terminal of the input coil connected to the grid of one vacuum tube, the other terminal of the input coil connected to the grid of a second vacuum tube, a tuning condenser in parallel with the input coil, a connection between the central tap of the input coil and the filaments of the vacuum tubes including the secondary of an audio transformer, the plates of the first and second vacuum tube connected together through an inductance, a tuning condenser in parallel with the inductance, a tap centrally located with respect to the terminals of the inductance, a connection from the tap through an indicating device and a source of plate power to the filaments of the vacuum tubes,

an inductance coupled to the inductance in the plate circuits of the first and second vacuum tubes, a tuning condenser for this lnductance, one terminal of th1s inductance coupled to the grid of a third vacuum tube functioning as a detector, the other terminal of this inductance connected to the filaments of the vacuum tubes and the plate of the detector tube connected through the primary of the audio frequency transformer and the source of plate power to the filaments of the vacuum tube.

6. In a' receiving and amplifying system including a plurality of vacuum tubes having filaments, grids and plates and sources of power therefor, the combination of an input coil having a central tap, one terminal of the input coil connected to the grid of one vacuum tube, the other terminal of the input coil connected to the grid of a second vacuum tube, a plurality of tuning condensers in parallel with the lnput'coil, a connection between the central tap of the input coil and the filaments of the vacuum tubes including the secondary of an audio transformer, the plates of the first and secondvacuum tube connected together through a plurality of inductances, a plurality of tuning condensers in parallel with the indiu-tances, a tap between the induetances. a connection from the tap through anfiindieating device and a source of plate current to the filaments of the vacuum tubes, a pluralit-y of inductances coupled to the induc- .through'the primary of the audio'frequency transformer and the source of plate power to the filaments of the vacuum tubes.

7. In a receiving and amplifying system including a plurality of vacuum tubes having filaments, grids and plates and sources of power therefor, the combination of an input coil having a central tap, one terminal of the input coil connected to the grid of one vacuum tube, the other terminal of the input coil connected to the grid of a second vacuum tube, a plurality of tuning condensers in parallel with the input coil, the central element of the tuning condensers being grounded, a connection between the central tap of the input coil and the grounded filaments of the vacuum tubes including the secondary of an audio transformer, the plates of the first and second vacuum tubes being connected together through an inductance, a tuning condenser in parallel with the inductance, a tap centrally located with re spect to the terminals of the inductance,a

. connect-ion from the tap through an indicating-device and a source of plate current to the filaments of the vacuum tubes, an inductance coupled to the inductance in the plate circuits of the first and second vacuum tubes,

a tuning condenser for this inductance, one

terminal of this inductance coupled to the grid of a third vacuum tube functioning as a'detector, the other terminal of this inductance connected to the filaments of the vacuum tubes and the plate of the detector tube connected through the primary of the audio frequency transformer .and the source of plate power to the filaments of the vacuum tubes.

8. In a. receivi-n and amplifying system including a plurality of vacuum tubes having filaments, grids and plates and source of power therefor, the combination of an inputcoil having a central tap, one terminal of the input coil connected to the grid of one vacuum tube, the other terminal of the input coil connected to the grid of a second vacuum tube, a tuning condenser in parallel with the input coil, a connection between the central tap of the input coil and the filaments of the vaccum tubes including the secondary of an audio transformer, the plates of the first and second vacuum tubes being connected together through an inductance, two resistances anda second inductance, a plurality of tuning condensers in parallel with the inductances and resistances, a tap between the resistances, a. connection from the tap through an indicating device and a source of plate current to the filaments of the vacuum tubes, a plurality of inductances coupled to the inductances in the plate circuits of the first and second vacuum tubes, a tuning condenser for these inductances, one terminal of these inductances coupled to the grid of a third'vacuum tube functioning as a detector, the other terminal of these inductances connected to the filaments of the vacuum tubes and the plate of the detector tube connected through the primary of the audio frequency transformer and the source of plate power to the filaments of the vacuum tubes. I

JAMES E. PARKER. 

